1. Field of the Invention
Exemplary aspects of the present disclosure generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof, and more particularly, to an optical scanner and an image forming apparatus including the optical scanner.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member (which may, for example, be a photosensitive drum); an optical scanner projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
Generally, the optical scanner includes a light source unit that projects a modulated light beam based on an image signal. The projected light beam is deflected and scanned by a rotary polygon mirror and focused onto the image bearing member via a focusing lens and a folding mirror, thereby forming an electrostatic latent image on the surface of the image bearing member.
A part of the light beam deflected by the rotary polygon mirror is separated into a scan-start signal and a scan-end signal by the folding mirror and strikes a light detector. Accordingly, the light beam is converted to an electric trigger signal. For overall size reduction of the optical scanner or to illuminate a target with a light beam at a desired angle, there is known an optical scanner equipped with the folding mirror inside the optical scanner to reflect the light beam.
More specifically, in order to reflect the light beam deflected by a deflector using the rotary polygon mirror toward the target, the folding mirror is generally long in a main scanning direction of the deflector. One end of such a long folding mirror is supported at two points, and the other end is held at a single point, thereby keeping the folding mirror flat even when the folding mirror is mounted in the optical scanner, such as in JP-H10-20628-A.
These two supporting points at one end of the folding mirror are each disposed a certain distance from end portions of the folding mirror in a short-side direction. One supporting point at the other end of the folding mirror in the longitudinal direction is disposed substantially at the center of the folding mirror in the short-side direction.
A drawback to this approach is that the folding mirror held in the above described manner still vibrates rotationally due to vibrations generated by a drive source in the image forming apparatus. As a result, image defects such as banding appear in a resulting image.
In view of the above, in another approach, the reflective mirror such as the folding mirror is adhered to a mirror holder using an adhesive. In this configuration, according to JP-H06-337342-A, the mirror holder includes a panel with holes, one of which includes a projection that supports a reflecting surface of the mirror. The other side of the reflecting surface is pressed by an elastic member. The projection of the hole of the panel of the holder and a portion of the reflective mirror that presses the hole of the panel of the holder are adhered using the adhesive. Further, the thickness of the adhesive portion is thinner than the thickness of the mirror so that when the adhesive is cured and shrunk, angular displacement of the mirror is suppressed.
Still another approach for suppressing rotational vibration of the reflective mirror is one in which a portion of the panel of the holder pressed by the reflective mirror includes an elastic member such as rubber, and the reflective mirror is pressed against the elastic member from the opposite side of the elastic member, instead of using an adhesive.
In another approach, a side surface of the reflective mirror is adhered using an adhesive.
Although advantageous, use of adhesive involves adjustment of the amount of adhesive, securing sufficient curing time, prevention of contamination of the mirror by the adhesive, and so forth. Consequently, when using the adhesive, special attention needs to be paid, complicating the assembly of the mirror.
In view of the above, there is thus an unsolved need for the image forming apparatus that can suppress rotational vibration of the mirror without using an adhesive and thus maintain the orientation of the mirror even when other devices vibrate.